Definitions: As used in this description and in any accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires:
The term “metal” is used herein to refer to a material composed of any element(s) belonging to the group of elements that, in their neutral ground state electronic configurations, readily lose one or more electrons to form positive ions. Without limitation, “metal” may refer to either a pure metal or alloy.
The term “predominantly non-metallic” denotes a material composition in which metals comprise only small fractions (<10%), including also trace fractions, by volume of the composition of a sample.
The term “mixed composition” denotes a collection of material, whether spatially homogeneous in composition or otherwise, wherein an appreciable fraction (>10%), by volume, of the material is metallic, and an appreciable fraction (>10%), by volume, of the material is non-metallic. The term “mixed composition”, in its adjectival sense, is used herein interchangeably with the term “inhomogeneous.”
The term “alloy” refers to a material that is predominantly metallic, and that is composed of more than a single element.
The term “complete spectral analysis” refers to a spectroscopic procedure wherein substantially all the x-ray fluorescence lines emitted by a sample within a specified range of the electromagnetic spectrum, and exceeding a specified signal strength, are employed to derive an estimate of the elemental composition of the sample. Other spectral features, other than lines, such as the shape of a scattering continuum, encompassing a portion (including the entirety) of the specified spectral range, may also be included, without limitation, in the complete spectral analysis. If only a small subset of lines within the specified spectral range is taken into account, then any resulting spectral analysis is not a “complete spectral analysis” within the meaning of the term as employed herein.
Current Practice: Field-portable x-ray fluorescence (XRF) instruments are used by inspectors throughout the world to determine the elemental distributions in a wide variety of sample matrices including soils, minerals, ceramics, metals, polymers, thin films, and paint on different substrates. The Thermo Scientific NITON® XL3, for example, employs various algorithms to properly analyze these different sample matrices. In general, a given instrument will be used in a specific instance for the analysis of a single class of samples, for example, sorting of alloys or the analysis of soil samples, or analysis of the paint in houses. In such cases, the most effective use of the analyzer is to operate in a single mode that the user selects from a menu on a touch screen or an associated computer.
There are, however, applications, in particular the measurement of toxic elements in consumer products, where any given product may contain several, or more, different materials. A costumed plastic doll is an example of a toy that may have cloth, leather-looking PVC parts, ceramic, and painted metal buttons. To obtain the correct analysis for each of these different materials requires the use of the correct settings of the XL3 and its corresponding analytic algorithms. Incorrect results will generally be reported if the wrong mode is chosen.
The most effective mode is often not obvious to the user, especially one not highly trained. For example, it may not be readily apparent to the user which of the available modes should be selected (which will typically be limited to a Metals Mode and a Plastics Mode) when inspecting items such as wood, fabric and foodstuffs. While the Plastics Mode is the most effective for analysis in such cases because all these materials are predominantly hydrocarbons, the user may be unlikely to know this fact.
XRF analyzers that determine the elemental concentration in materials make use of sophisticated analytic tools. To carry out the computational analysis as expeditiously as possible, it is normal practice to have the user cue the instrument as to the type of material dominating the object to be analyzed. In various Thermo Niton XRF analyzers, for example, cueing is performed by touching the appropriate icon, such as, for example, either “alloy” or “plastic,” on a touch screen. Computer algorithms, starting with the generic information provided by the user, further refine the parameter space of analysis on the basis of the spectrum being collected. For example, the measurement of a metal, pre-designated by the user, will be sorted prior to full analysis as iron based, or copper based or zinc based depending on the strengths of the characteristic x-ray lines of iron, or copper or zinc. And the spectrum itself, by virtue of identified features, automatically allows the algorithm to select between polyvinyl chloride (PVC), for example, where chlorine is present, and other plastics that contain no major element heavier than oxygen.
U.S. Pat. No. 7,170,970 (to Tani et al.) teaches an automated algorithm to “[identify] or [judge]” whether the material is a “metal” or a “non-metal” on the basis of whether—or not—the sample emits fluorescent X-ray lines with a high spectrum intensity in response to short-time irradiation by x-rays. The pertinent teaching is found in col. 4, lines 1-10, of the patent of Tani et al. This method, while useful for certain prescribed applications, may not be well-suited to inspection of a broader range of materials of unknown composition.
Another patent, U.S. Pat. No. 7,430,274 (to Connors et al.), describes an inspection modality wherein an initial test is performed under a first setting of beam energy endpoint and beam filtration, and rates are determined for detected Compton scattering and fluorescence in a denumerated set of metal lines relative to the total detected count rate. Then, contingent upon a preliminary classification of the resulting detection, beam current is varied, and then one of a number of possible filters in inserted into the beam for subsequent measurements. This inspection modality will be referred to herein as a “contingent setting” inspection modality, since the set of beam and filter conditions under which final measurements are made is entirely contingent on the results of a first set of measurements.